US 6690533 B2 Abstract The present invention provides a method to determine and to locate the position of the imbalance torque of an actuator in a disc drive. There are several steps performing different functions in the method. The first step of the method performs the function of obtaining a difference in the voice coil motor (VCM) current of the disc drive in the X orientation and in the Y orientation with the VCM current of the disc drive when the disc drive is placed flat. The second step performs the function of obtaining the square of each difference in VCM current. The third step performs the function of obtaining the imbalance by adding the square of the VCM current and subsequent square root of the addition. The valve of the imbalance torque is obtained by multiplying the imbalance with the torque constant. The fourth step performs the function of obtaining a division value of the VCM current in the X orientation or in the Y orientation with the VCM current of the disc drive when the disc drive is placed flat. The fifth step performs the function of obtaining the angle between the x-axis and the distance of the imbalance torque of the actuator from the pivot centre and measuring the mass of the actuator. The sixth step performs the function of obtaining the cosine or sine of the angle and multiple either angle with the mass of the actuator. The position of the imbalance torque is located and determined either from dividing the divided value in X orientation in the fourth step with the cosine angle in the sixth step or dividing the divided value in Y orientation in the fourth step with the sine angle in the sixth step.
Claims(14) 1. A method for determining an imbalance torque of an actuator in a disc drive, the actuator being configured to be rotated about a pivot point by a voice coil motor (VCM), the VCM being operable by a VCM current, the imbalance torque being characterized by a center of imbalance and a magnitude of imbalance, the method comprising steps of:
(a) obtaining an X orientation VCM current (X
_{ivcm}) when the disc drive is placed in an X orientation plane, wherein the X orientation plane is characterized by a normal parallel to an X-axis; (b) obtaining a horizontal orientation VCM current (F
_{ivcm}) when the disc drive is placed in a horizontal plane characterized by a vertical normal; wherein the X-axis and the vertical, axis are orthogonal to one another; (c) obtaining a first difference between the X orientation VCM current and the horizontal orientation VCM current; and
(d) obtaining the magnitude of the imbalance torque from the first difference.
2. The method of
3. The method of
(e) obtaining a Y orientation VCM current (Y
_{ivcm}) when the disc drive is placed in a Y orientation plane, wherein the Y orientation plane is characterized by a normal parallel to a Y-axis, and wherein the X-axis, the Y-axis and the vertical axis are orthogonal to one another; (f) obtaining a second difference between the Y orientation VCM current and the horizontal orientation VCM current;
(g) adding together the square of the first difference and the square of the second difference to give a first intermediate value;
(h) obtaining the square root of the first intermediate value to give an imbalance value; and wherein the step (d) includes a step (i) of multiplying the imbalance value with a torque constant to obtain the magnitude of imbalance.
4. The method of
(j) dividing the Y orientation VCM current value by the X orientation VCM current value to obtain a second intermediate value; and
(k) applying a predetermined function to the second intermediate value to obtain an angle, such that the angle is representative of an angular displacement of the center of imbalance from the X-axis.
5. The method of
(l) applying a cosine function to the angle obtained in step (k) to give a third intermediate value;
(m) multiplying the mass of the actuator with the third intermediate value to obtain a fourth intermediate value; and
(n) dividing the X orientation VCM current with the third intermediate value to determine a displacement of the imbalance torque center from the pivot point.
6. The method of
(l) applying a sine function to the angle obtained in step (k) to give a third intermediate value;
(m) multiplying the mass of the actuator with the third intermediate value to obtain a fourth intermediate value; and
(n) dividing the Y orientation VCM current with the third intermediate value to determine a displacement of the imbalance torque center from the pivot point.
7. A program storage device readable by a computer system tangibly embodying a program of instructions executable by the computer system to perform a method for determining an imbalance torque of an actuator in a disc drive, the actuator being configured to be rotated about a pivot point by a voice coil motor (VCM), the VCM being operable by a VCM current, the imbalance torque being characterized by a center of imbalance and a magnitude of imbalance, the method comprising steps of:
(a) obtaining an X orientation VCM current (X
_{ivcm}) when the disc drive is placed in an X orientation plane, wherein the X orientation plane is characterized by a normal parallel to an X-axis; (b) obtaining a horizontal orientation VCM current (F
_{ivcm}) when the disc drive is placed in a horizontal plane characterized by a vertical normal; wherein the X-axis and the vertical axis are orthogonal to one another; (c) obtaining a first difference between the X orientation VCM current and the horizontal orientation VCM current; and
(d) obtaining the magnitude of the imbalance torque from the first difference.
8. The method of
9. The method of
(e) obtaining a Y orientation VCM current (Y
_{ivcm}) when the disc drive is placed in a Y orientation plane, wherein the Y orientation plane is characterized by a normal parallel to a Y-axis, and wherein the X-axis, the Y-axis and the vertical axis are orthogonal to one another; (f) obtaining a second difference between the Y orientation VCM current and the horizontal orientation VCM current;
(g) adding together the square of the first difference and the square of the second difference to give a first intermediate value;
(h) obtaining the square root of the first intermediate value to give an imbalance value; and wherein the step (d) includes a step (i) of multiplying the imbalance value with a torque constant to obtain the magnitude of imbalance.
10. The method of
(j) dividing the Y orientation VCM current value by the X orientation VCM current value to obtain a second intermediate value; and
(k) applying a predetermined function to the second intermediate value to obtain an angle, such that the angle is representative of an angular displacement of the center of imbalance from the X-axis.
11. The method of
(l) applying a cosine function to the angle obtained in step (k) to give a third intermediate value;
(m) multiplying the mass of the actuator with the third intermediate value to obtain a fourth intermediate value; and
(n) dividing the first VCM current with the third intermediate value to determine a displacement of the imbalance torque center from the pivot point.
12. The method of
(l) applying a sine function to the angle obtained in step (k) to give a third intermediate value;
(n) dividing the Y orientation VCM current with the third intermediate value to determine a displacement of the imbalance torque center from the pivot point.
13. The method of
(o) estimating the position of the center of imbalance to be in a first quadrant if Y
_{ivcm }is greater than F_{ivcm }and if X_{ivcm }is greater than F_{ivcm}; (p) estimating the position of the center of imbalance to be in a second quadrant if Y
_{ivcm }is less than F_{ivcm }and if X_{ivcm }is greater than F_{ivcm}; (q) estimating the position of the center of imbalance to be in a third quadrant if Y
_{ivcm }is lesser than F_{ivcm }and X_{ivcm }is less than F_{ivcm}; and (r) estimating the position of the center of imbalance to be in a fourth quadrant if Y
_{ivcm }is greater than F_{ivcm }and if X_{ivcm }is less than F_{ivcm}, wherein the disc drive is placed in the horizontal plane with the pivot point coinciding with the intersection of the X-axis and the Y-axis, and wherein the first quadrant, the second quadrant, the third quadrant and the fourth quadrants are defined with reference to the X-axis and the Y-axis. 14. A disc drive comprising:
a disc formatted to store data;
a transducer head configured for reading data from and writing data to the disc;
an actuator supporting the transducer head in proximity to the disc; and
means for determining an imbalance torque of the actuator.
Description This application claims the benefit of U.S. Provisional Application No. 60/184,699, filed Feb. 24, 2000. The present invention relates generally to disc drives, and more particularly to determine the actuator imbalance torque as well as to locate the position of the imbalance torque. The track following servo systems in disc drives are required to hold the read/write heads to very small off-track errors to support the increasing track density of today's products. As errors can be induced due to many effects including disc and bearing runout, servo-track-writer induced irregularities, electronic noise, spindle and actuator resonances, and external shock and vibration excitations, modern disc drives must be designed and tested to perform satisfactorily to increasingly stringent specifications of shock and vibration. This is especially due to the needs of the portable computing market. Thus, there exists a need to be able to predict track following performance under external shock and vibration excitation. The ability to measure the actuator imbalance will be a good indication of the drive performance under shock and vibration condition. In the existing setup to measure imbalance torque, the actuator is held to be free to rotate about its cartridge centre which is the pivot point and a load cell is located one inch from this point. The distance from the pivot point to the load cell multiplied by the force to move the actuator will give the imbalance torque. However, there are problems in using this method. Firstly, there is a need to remove the flex cable since it will contribute to the actuator an additional imbalance during measurement. Secondly, the location of the load cell may not be accurate enough to obtain a good measurement. Thirdly, the measurement could only be carried out at the component level. Thus there remains a need for a more accurate and sophisticated method to determine the imbalance torque. It will be evident from the following description that the present invention offers this and other advantages. The present invention relates to a more accurate method of determining the imbalance torque of an actuator in a disc drive at drive level and of locating the position of the imbalance torque using voice coil motor bias current values so as to diagnose the mechanical and servo performances of the disc drive. According to one aspect of the invention, there is provided a method to sense the change in the voice coil motor (VCM) current to determine and to locate the position of the imbalance torque of an actuator in a disc drive. There are several steps performing different functions in the method. The first step of the method performs the function of obtaining a difference in the VCM current of the disc drive in the X orientation and in the Y orientation with the VCM current of the disc drive when the disc drive is placed flat. The second step performs the function of obtaining the square of each difference in VCM current. The third step performs the function of obtaining the imbalance current by adding the square of the VCM current and subsequent square root of the addition. The value of the imbalance torque is obtained by multiplying the imbalance current with the torque constant of the voice coil magnet. The fourth step performs the function of obtaining a division value of the VCM current in the X orientation or in the Y orientation with the VCM current of the disc drive when the disc drive is placed flat. The fifth step performs the function of obtaining the angle between the x-axis and the distance of the imbalance torque of the actuator from the pivot centre and measuring the mass of the actuator. The sixth step performs the function of obtaining the cosine or sine of the angle and multiple either angle with the mass of the actuator. The position of the imbalance torque of the actuator is located and determined either from dividing the divided value in X orientation in the fourth step with the cosine angle in the sixth step or dividing the divided value in Y orientation in the fourth step with the sine angle in the sixth step. These and other features as well as advantages, which characterize the present invention, will be apparent upon reading of the following detailed description and review of the associated drawings. FIG. 1 is an exploded view of a typical disc drive. FIG. 2 shows a simplified top view of a disc drive in an X orientation, according to the present invention. FIG. 3 shows a simplified top view of a disc drive in an Y orientation, according to the present invention. FIG. 4 shows a simplified top view of a disc drive placed flat in a third orientation, according to the present invention. FIG. 5 shows a simplified top view of an actuator for locating the position of the imbalance torque of the actuator in the present invention. FIG. 6 shows a simplified top view of an actuator showing four possible zones where the imbalance torque of the actuator may be located. FIG. 7 shows a flowchart of a disc drive configured in track following mode. FIG. 1 shows an exploded view of a typical disc drive When the disc drive is in a track following mode, an amount of current (F A preferred embodiment of the present invention is now described as follows with reference to FIGS. 2 to Due to the changes in VCM current, the following equations are applied to calculate the imbalance torque
where K With the values of Y where Y Since θ can be calculated from the above equation and mass, m, of the actuator can be measured, the distance of the imbalance torque from the pivot centre
This method is implemented into a software program and tested on a disc drive as illustrated in FIG. From the valves of Y (a) If Y (b) If Y (c) If Y (d) If Y The portions are defined with respect to a pair of X and Y-axes intersecting at the pivot point of the actuator. The portion A refers to the fourth quadrant, the portion B refers to the second quadrant, the portion C refers to the first quadrant and the portion D refers to the third quadrant in this frame of reference. In another embodiment of the method to determine the imbalance torque, the disc drive is placed in a position with the use of an external fixture such that the actuator is in a first plane and the VCM current, X
where K Another way of describing the present invention is as follows: A program storage device readable by a computer system tangibly embodying a program of instructions executable by the computer system to perform a method for determining an imbalance torque of an actuator According to one embodiment of the invention, the first difference is multiplied by a torque constant to obtain the magnitude of imbalance. According to another embodiment of the invention, the method further involves obtaining a second VCM current (Y Preferably, the method further involves steps of: dividing the second VCM current value by the first VCM current value to obtain a second intermediate value; and applying a predetermined function to the second intermediate value to obtain an angle, such that the angle is representative of an angular displacement of the center of imbalance from the X-axis. The method can further involve steps of applying a cosine function to the angle obtained to give a third intermediate value; multiplying the mass of the actuator with the third intermediate value to obtain a fourth intermediate value; and dividing the first VCM current with the third intermediate value to determine a displacement of the imbalance torque center from the pivot point. Alternatively, the method can further involve steps of applying a sine function to the angle obtained to give a third intermediate value; multiplying the mass of the actuator with the third intermediate value to obtain a fourth intermediate value; and dividing the second VCM current with the third intermediate value to determine a displacement of the imbalance torque center from the pivot point. According to one aspect of the invention, the method provides for estimating the position of the center of imbalance. The center of imbalance is estimated to be in a first quadrant if Y It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this disclosure is illustratively only, and changes may be made in detail, especially in the matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the particular elements may vary depending on the particular application for the disc drive while maintaining substantially the same functionality without departing from the scope and spirit of the present invention. In addition, although the preferred embodiment described herein is directed to a disc drive, it will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other systems, without departing from the scope and spirit of the present invention. Patent Citations
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